Separate pumps to produce different pressures in different circuits are known. Likewise, pumps are known which provide two pressures for two hydraulic circuits. Such pumps, however, may require separate controls to pressurize each circuit. Accordingly, such controls may be confusing to operate particularly if the operator is unskilled.
In a control system for opening and closing a downhole surface controlled subsurface safety valve (SCSSV) and a surface safety valve (SSV), there are three fluid pressures. First, there is control pressure used for the fluid in the control system used in the shutdown of the surface controlled subsurface safety valve after the closure of the surface safety valve. The control circuit pressure is at the low end of the pressure range relative to the pressures in the remaining circuits, typically being up to approximately 150 psi. Second, there is fluid pressure used to maintain the surface controlled subsurface safety valve in its open configuration under operating conditions. This fluid is maintained at the high end of the pressure range, typically being between 5000-10000 psi. Third, there is the fluid pressure used to maintain the surface safety valve in its open condition. The fluid in this circuit is typically within a pressure range of 1000-3500 psi.
The higher the fluid pressure required, the smaller the piston of the pump that is used to pressurize the circuit. Therefore, different pistons have typically been used to supply the necessary fluid to the different circuits. A larger piston may be used to supply control pressure fluid and to supply fluid to the surface safety valve circuit. A smaller piston may be used for supplying fluid to the circuit of the surface controlled subsurface safety valve.